Multispectral imaging as digital restoration tool for faded inks on manuscripts. Three cases of study of degraded written parchments by means of non-destructive techniques

In the study of manuscripts, the scientific researches are generally oriented to the chemical analysis of the inks, parchments or papers and restoration materials and, only in last 15 years, the application of multispectral imaging appears in the scientific literature. Multispectral Imaging has been developed by combining digital imaging and spectroscopy. The multispectral imaging shows higher performance then a color digital camera due to the fact that reveals light portions and/or infrared wavelengths that cannot be detected by the human eye. The spectral images may aid paleographers to read old scripts by enhancing the contrast between the under-and-overwriting or inks that are partially or completely disappeared. We present a non-destructive study of three written parchments, partially degraded, stored at Library of Department of History, Cultures and Religions at Sapienza-University (Rome): “Provvisorio 34 bis 8839/c” (XIV century), “Provvisorio 37 8839/o e 8839/t” ( XIV secolo ) and “Provvisorio 38”(containing a Filocolo fragment by Giovanni Boccaccio). The manuscripts have been analyzed by means of X-ray Fluorescence (XRF), Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), reflectance spectroscopy, multispectral UV fluorescence imaging, VIS-NIR multispectral imaging and radiography. The three manuscripts have been written with iron gall inks, while the capital letters have been realized with cinnabar (or vermillion) and azurite. The presence of gypsum on some areas of the parchment of the “Provvisiorio 34” indicates that the sulphate ions of the ink are migrated in the support. By illuminating the manuscripts with visible sources, the acquisition of multispectral images with narrow interferential filters, permits the maximization of the contrast between the inks and the parchment leading to read the leaching areas of the manuscripts. With the same approach, by exciting with UV lamps, it is possible to read faded inks, by exploiting the fluorescence phenomenon of the parchments and, in general, of the organic matters. Moreover, the radiography technique was employed to verify the possibility to read inside multilayer structures, as overlapping written parchments, demonstrating that red capital letter (containing elements of high-atomic number) are detectable.